1. Field of the Disclosure
The present invention relates generally to sampling of electronic values and, more particularly, the present invention relates to storage of sample values.
2. Background
Electronic sampling is used by many electronic systems. Well known applications include applications such as audio, data acquisition, control, and the like. In some applications, a sampled value may need to be held for a relatively long period of time. For example, during regulation of a power supply, an analog peak input voltage may need to be detected. The sampled value may need to be held for a relatively long period of time (e.g., 10 ms). A sample and hold circuit can operate by converting the signal value to a current, which is then used to charge a capacitor so the sample can be stored. A switch can be used to selectively control when the capacitor is used to sample. In particular, the switch may be closed to allow the capacitor to charge, and opened to allow the capacitor to retain the sampled charge. The switch may also be closed again to release the sampled charge from the capacitor.
However, when using this particular sample and hold technique on an integrated circuit, there is normally a leakage current flowing through the switch, such that the amount of charge stored in the capacitor changes. For example, leakage current can cause additional charge to flow into and to be stored by the storage capacitor even after the switch has been opened. As the length of time that the value has been stored increases, the stored value increases due to additional charge buildup. When the stored charge has been held for a substantial time, the stored value may no longer be an accurate representation of the initially sampled value because of the additional charge buildup resulting from the leakage current. In another example, leakage current may flow from the capacitor and charge may flow out of the capacitor as duration of time increases, thus making the stored value substantially less than the initially sampled value after a longer time duration.
The effect of leakage current on the stored charge can be reduced by increasing the capacitance of the storage capacity. However, the resulting increased size of the capacitor can result in correspondingly higher costs for integrated circuit that incorporates the increased size capacitors. The effect of leakage current on the storage charge can also be reduced by improving the design of the storage capacitor. However, the improved design typically results in higher design and processing costs for manufacturing the integrated circuit that incorporates the capacitors having an improved design. As can be seen, these approaches generally increase costs and/or size of the circuit design.